I think the skew heap I have needs some work, because it seems to come only from Okasaki's code example, so it doesn't take into consideration his suggestions/exercises. So, only insert is O(1), and the min would need to be stored separately to get O(1) instead of O(log(N)). He had a suggestion for making the merge of two heaps O(1), but I wasn't as concerned about that operation. It seems hard to get an "out" operation that is O(1) amortized, that is removing the min from the heap (hopefully O(log(N)) worst case). I will look at testing a heap implementation to see how it might work out. Thanks for the information.
On 11/09/2011 01:00 AM, Ulf Wiger wrote:
>> Yeah, obviously, mine was just a sketch, thrown down as an executable comment and optimized for brevity. :)
>> (Although I'm not convinced, from reading, that Michael's implementation is faster than mine. Anyone who cares deeply enough could of course measure. I am currently not shopping for a faster priority queue, so I will pass on that.)
>> As an aside, it was a simple skew heap exercise, presented by Chris Okasaki, that made me invite Quviq to Ericsson for the first Erlang QuickCheck pilots.
>> The task was to reverse-engineer the insertion order of a particular skew heap. John Hughes solved it with a "brute force approach", using QuickCheck to test his assumptions. Watching him do exploratory hacking with QuickCheck was so much fun that, once he ported QuickCheck to Erlang, I had to try to find out if it could be put to use in a commercial project.
>> Unfortunately - or fortunately - for Quviq, the only candidate for a useful pilot was stateful, and QuickCheck had no support for that. For lesser minds, that might have been a problem, but John and Thomas quickly invented the statem model. :)
>> BR,
> Ulf W
>> On 9 Nov 2011, at 09:45, Zabrane Mickael wrote:
>>> Hi Ulf,
>>>> Michael Truog already has a SkewBinHeap impelmentation here:
>>https://github.com/okeuday/skewbinheap>>>> Regards,
>> Zabrane
>>>> On Nov 9, 2011, at 9:42 AM, Ulf Wiger wrote:
>>>>> I'm partial to skew heaps, mainly because they are so elegant.
>>>>>>http://www.cse.yorku.ca/~andy/courses/4101/lecture-notes/LN5.pdf <http://www.cse.yorku.ca/%7Eandy/courses/4101/lecture-notes/LN5.pdf>
>>>>>> Something like this (although I've done only basic testing):
>>>>>> -module(skew).
>>> -export([new/0, in/2, out/1]).
>>>>>> new() ->
>>> [].
>>>>>> in(X, Heap) ->
>>> merge({X,[],[]}, Heap).
>>>>>> out([]) ->
>>> error;
>>> out({X, L, R}) ->
>>> {X, merge(L, R)}.
>>>>>> merge({P0,Pl,Pr}, {Q0,_,_} = Q) when P0 < Q0 ->
>>> {P0, Pr, merge(Pl,Q)};
>>> merge({P0,_,_} = P, {Q0,Ql,Qr}) when P0 > Q0 ->
>>> {Q0, Qr, merge(Ql,P)};
>>> merge({P0,Pl,Pr} = P,{P0,Ql,Qr}) -> % equal roots
>>> merge(P, merge(merge(Pl,Pr), merge(Ql,Qr)));
>>> merge([], Q) -> Q;
>>> merge(P, []) -> P.
>>>>>> The cost is amortized O(log N) for in/2 and out/1. For peeking at the min, it's O(1).
>>>>>> BR,
>>> Ulf W
>>>>>> On 9 Nov 2011, at 04:33, Michael Truog wrote:
>>>>>>> I was looking at Erlang priority queue implementations and the Riak/RabbitMQ one seemed a bit slow. I have a different implementation with the same API here: https://github.com/okeuday/pqueue/blob/master/src/pqueue.erl>>>>>>>> The results from my test are here: http://okeuday.livejournal.com/19187.html>>>>>>>> The implementation has "in" operations that are roughly 3 times faster (300%), however, the "out" operation became roughly 30% slower. So, as long as the priority queue is storing a decent amount of items, this data structure should provide better speed. The implementation is limited to a specific priority range: -20 (high) to 20 (low).
>>>> _______________________________________________
>>>> erlang-questions mailing list
>>>> <mailto:>
>>>>http://erlang.org/mailman/listinfo/erlang-questions>>>>>> Ulf Wiger, CTO, Erlang Solutions, Ltd.
>>>http://erlang-solutions.com <http://erlang-solutions.com/>
>>>>>>>>>>>> _______________________________________________
>>> erlang-questions mailing list
>>> <mailto:>
>>>http://erlang.org/mailman/listinfo/erlang-questions>>>>>>>> Ulf Wiger, CTO, Erlang Solutions, Ltd.
>http://erlang-solutions.com>>>
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